Fixed export/soundfiles.php

- .csv downloads are missing for #5
- Added js/models/SoundDownloader.js
- Added query/dataProvider.php
  - It encapsulates the functionality of query/data.php,
    so that data.php is cleaner, and the same functionality can be used
    outside of it without a need to parse JSON.
- query/data.php now also works from cli.
- Added a blacklist feature to query/data.php that makes it possible to only fetch a part of the structure.